This invention relates to magnetising members of magnetisable material.
In conventional methods of magnetising magnetisable material, an energised coil of wire is coupled with a member of magnetisable material, thereby causing the member to become magnetised or “energised” as a permanent magnet.
However there are problems associated with magnetising a plurality of adjacent members of unmagnetised magnetisable material. If all the members are to be magnetised simultaneously, an arrangement of many high energy coils would be needed, each carrying a large current so as to set up a strong magnetic field around each coil. Such an arrangement with high currents and strong magnetic fields may be disadvantageous in constituting a health and safety hazard. A more significant disadvantage is that such high energy apparatus is expensive to manufacture and to operate.
JP-A-62274608 discloses a method of magnetising magnetisable members so as to avoid those members having parts that are unmagnetised. Successive pairs of the members are magnetised, with each pair other than a first magnetised pair including one member of a respective previously magnetised pair, and the final pair to be magnetised including a member of the first pair. The method is such that each member is magnetised twice.
JP-A-62274608 recognises that such a method might result in an undesirable demagnetisation action being applied to some of the members, but states that this action would be resisted by the members and would have no effect thereon. This might be the case when magnetising a small number of spaced apart members, but demagnetisation would tend to occur if the method of JP-A-62274608 were used to magnetise a larger number of members, or members that were more closely juxtaposed so as to be susceptible to stray flux from magnetising means.
It is an object of this invention to address these problems.